How to adjust input sensitivity on a car audio amplifier.
Many people have asked me what is the correct way to adjust the input sensitivity
on a car audio amplifier. The right way is with an Oscilloscope (often referred to
as O-scope) but that's an expensive piece of equipment. Plus, if they have that
then they already know how to use it. This page instead will focus on the second
best method of using a Digital Multi-Meter (DMM) capable of reading AC Voltage.
What you need:
What to do:
- A CD (or other playable high-quality media) containing non-attenuated test tones
(0dB reference level) in the frequency range of the intended device. 40-80Hz for
most subs and 500-2000Hz for fill speakers for example.
- A Digital Multi-Meter (DMM) capable of reading AC Voltage (Vrms).
- A simple calculator (or the form on this page).
Now you have the maximum unclipped setting for the amp as you plan to wire it.
(maybe mark it with something for reference) From this point you can lower it
again for system balance if desired but do not go above this point.
- Figure out the Vrms to watch for with the Voltmeter using the following formula:
Vrms = Square_Root(Expected_Amp_Power_RMS * As-Wired_Impedance)
- Make or get the CD with the test tones. Here are some you can use:
- 50Hz (for most subs)
- 1kHz (for most fill speakers).
- Disconnect the speakers from the amp if they are already connected.
- Turn off all signal boosting, enhancing, or processing options on all equipment.
(I.E. Loudness, bass boost, etc..)
- Set any bass/treble or eq controls to middle or flat (0dB settings).
- Set the volume on the head unit to just below it's clipping state or 3/4 of full volume
if exact clipping state is not known.
- If the head unit has an option for specific channel control and it's not centered on 0dB,
set it to 3/4 it's rated capability.
- Set the input sensativity to the minimum setting.
- Connect the Voltmeter to the amp as the speakers would be wired.
- Play the corresponding test tone for the speakers you will be using.
- Adjust the input sensitivity until the voltage reads the expected output.
- Reattach the speakers.
- 4V is a lower setting than 1V on an input adjustment marked with voltages.
- The test tones are saved in ZIP format. You will need to extract them.
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